CARA 2.0 – "I Built a Better Robot Dog"
2 days ago
- #quadruped
- #robotics
- #DIY
- The author built CARA 2.0, an upgraded version of their quadrupedal robot, as a senior design project with goals of low cost (<$1000) and low weight (<20lbs).
- To reduce costs, they developed a low-cost Quasi Direct Drive (QDD) actuator using a TYI 5008 BLDC motor ($18) and MKS XDrive Mini FOC controller ($41), but rewound the motor to lower its KV from 335 to 90 for higher torque.
- Issues with the XDrive controller's CAN bus communication were resolved using custom firmware from Mohammad Marshid, enabling stable motor control and feedback.
- A capstan drive joint test stand was prototyped, weighing 470g with a 9.6:1 reduction, 12 Nm peak torque, and 120° range of motion, using Dyneema rope and prestretching for assembly.
- The leg design features a coaxial 5-bar linkage with a 2:3 upper-to-lower link ratio for improved range of motion and aesthetics, and uses squash balls for compliant, traction-rich feet instead of TPU.
- Full robot design centralized electronics in a top-mounted e-box, used 3D-printed PLA frames to cut costs, and proper CAN bus wiring with 120 Ω resistors for reliability.
- Gait programming uses a trotting sequence with cycloid step trajectories, but initial walking issues due to asymmetrical legs were fixed by redesigning legs for symmetry.
- Turning and dynamic stability were improved over CARA 1.0 by stepping at 45° angles for turning and shifting the center of mass on inclines, rather than relying on IMU-based rotation.
- Final specs include a cost of $1,450, weight of 18.2 lbs, walking speed of 0.55 m/s, payload capacity of 15 lbs, and 1-hour runtime, making it a low-cost, dynamic quadruped for hobbyists.
- The author considers CARA 2.0 a success but notes capstan drives are assembly-unfriendly and plans to use off-the-shelf actuators in future robots, retiring this project.